The present invention relates to regular-shaped particles of activated clay, to a method of producing the same and to use thereof. More particularly, the invention relates to regular-shaped clay particles of activated clay comprising an acid-treated product of a dioctahedral smectite having macropores in the particles, having excellent adsorbing property and filtering property in combination, and exhibiting excellent decolorizing performance and catalytic performance, to a method of producing the same and to use thereof.
It has been known from the old times that dioctahedral smectite clay minerals exhibit adsorbing property and decolorizing property. In Great Britain, these minerals have also been called fuller""s earth or bleaching earth.
It has also been known from the old times to produce the so-called activated clay having increased specific surface areas by treating dioctahedral smectite clay minerals with an acid. For example, Japanese Examined Patent Publication (Kokoku) No. 335/1948 discloses a method of producing activated clay by kneading and molding acidic clay or a similar clay in water into a size of from 0.5 to 30 mm not to collapse, introducing resulting clay into an acid-resistant container, and heating and circulating an inorganic acid therein to activate the clay.
Japanese Examined Patent Publication (Kokoku) No. 2960/1957 discloses a method of producing granular activated clay by adding sulfuric acid to acidic clay to shape it and, then, drying until it can be milled, followed by milling, sieving to trap the particles of predetermined sizes and activating the particles in a customary manner.
Japanese Examined Patent Publication (Kokoku) No. 11209/1970 discloses a method of treating alumina silicate clay to produce activated clay or fine powdery silica by treating alumina silicate clay containing acid-soluble basic components with an acid, wherein the alumina silicate clay is added an acidic aqueous solution in an amount of not larger than the amount of an acidic aqueous solution with which clay particles in a dispersion starts precipitating, the clay particles being formed in the dispersion due to the addition of an acid, or an acid in an amount of from 1.0 to 1.5 equivalents with respect to the basic metal components that are to be removed, the basic metal components in the clay are reacted with the acid in the dispersion and, then, the reaction product is isolated from the dispersion solution, the particles of the reaction product are treated in an aqueous medium at a pH of not larger than 1, and the basic metal components are picked up from the product.
According to the conventional production of activated clay by the treatment with an acid, the treatment conditions are adjusted such as adjusting the acid concentration, temperature, treating time, etc. so that the acid-soluble basic components in the clay minerals are at least partly eluted to improve decolorizing performance and to increase the specific surface area.
Among the uses of activated clay, the use as a refining agent for oils and fats requires a strong property for adsorbing coloring matters such as chlorophyll and the like contained in fats or oils, as well as good filtering property for separating the refined fats and oils from the waste clay from the standpoint of production.
In the conventional activated clay, however, the property for adsorbing coloring matters is not compatible with the filtering property, and no clay has yet been known satisfying both of these properties to a sufficient degree.
That is, property for adsorbing coloring matters is improved as the particle diameter of the activated clay becomes more fine. On the other hand, the filtering property decreases to a conspicuous degree as the particle diameter becomes fine.
The present inventors have succeeded in producing regular-shaped particles of activated clay forming macropores therein, preserving fine structure of the dioctahedral smectite clay minerals, and having particle diameters controlled to lie within a range in which they exhibit excellent filtering property and have discovered the fact that the activated regular-shaped clay particles exhibit excellent adsorbing property and filtering property in combination.
The object of the present invention, therefore, is to provide activated regular-shaped clay particles obtained by treating a dioctaheral smectite with an acid, having macropores in the particles, having excellent adsorbing property and filtering property in combination, and exhibiting excellent decolorizing performance and catalytic performance, and a method of producing the same.
Another object of the present invention is to provide a method of easily and efficiently producing the activated regular-shaped clay particles having the above-mentioned properties without using any particular apparatus or means.
According to the present invention, there are provided activated regular-shaped clay particles obtained by treating dioctahedral smectite clay minerals with an acid, wherein the regular-shaped particles have a volume-based median diameter (D50) of from 10 to 60 xcexcm as found by a laser diffraction method, have a porous volume of porous radii of 1000 to 70,000 angstroms of from 0.63 to 1.00 cc/g as measured by a mercury intrusion porosity method, and have a BET specific surface area of from 250 to 400 m2/g.
It is desired that the activated regular-shaped clay particles have a circularity (A) defined by the following formula (1),
A={{square root over ( )}(R1xc3x97R2)}/R1xe2x80x83xe2x80x83(1)
wherein R1 represents the radius of a circumscribed circle along the contour of a particle of a scanning-type electron microphotograph thereof, and R2 represents the radius of an inscribed circle thereof, of from 0.8 to 1.0.
It is desired that the activated regular-shaped clay particles have a frill-like thin-piece texture specific to montmorillonite and crater-like porous texture in the scanning-type electron microphotograph thereof.
It is desired that the activated regular-shaped clay particles have a diffraction peak at 2xcex8=19 to 20 degrees specific to montmorillonite and a diffraction peak at 2xcex8=25 to 26 degrees specific to gypsum in the X-ray diffraction (Cuxe2x88x92xcexaxcex1).
According to the present invention, there is further provided a method of producing activated regular-shaped clay particles comprising the steps of:
adjusting the particle size of the dioctahedral smectite clay minerals to possess a volume-based median diameter (D50) of from 1 to 10 xcexcm as found by a laser diffraction method;
mixing an acid-soluble or acid-decomposing inorganic compound to the milled product thereof;
granulating the mixture into regular-shaped particles having a volume-based median diameter (D50) of from 10 to 60 xcexcm as found by a laser diffraction method; and
treating the regular-shaped particles with an acid while maintaining the particle shapes.
According to the method of production of the invention, it is desired that:
1. An acid-soluble or acid-decomposing inorganic compound is mixed to the milled product in an amount of from 1 to 15% by weight in terms of the dry product thereof;
2. the acid-decomposing inorganic compound is a calcium carbonate;
3. The mixture is granulated by subjecting a slurry of the mixture to a spray-dry granulation; and
4. The regular particles are treated with an acid by being immersed in an aqueous solution of a mineral acid maintained at 60 to 100xc2x0 C.
According to the present invention, there is further provided a refining agent for fats or oils, comprising the above-mentioned activated clay.
According to the present invention, there is further provided a catalyst carrier comprising the above-mentioned activated clay.